To address an important data gap, we propose to continue a longitudinal cohort study, the Fresno Asthmatic Children's Environment Study (FACES), funded by the California Air Resources Board for the last 5 years. The overall goal of the study is to determine if children with asthma who have adverse responses to short- term, daily increases in concentrations of ambient air pollutants and bioaerosols are more likely to have increased long-term asthma morbidity and decreased lung function growth. The specific aims of the study are the following: 1) to evaluate the long-term health effects of exposure to air pollutants/bioaerosols on symptoms, asthma severity, and growth of lung function;2) to evaluate the effect of interactions between exposures to traffic-related pollutants and bioaerosols on both short-term and long-term effects;3) to use new methods of causal analysis (marginal structural models) to address Alms 1 and 2, with comparison of quantitative inferences between causal and association analyses;and 4) to create a DNA specimen bank for future studies of the role of genes potentially involved in determining susceptibility of asthmatic individuals to short and long-term effects of exposures to oxidant air pollutants and/or bioaerosols. The overall design is a series of panel studies embedded within a longitudinal cohort study. The 14-day panel studies include twice- daily spirometry and symptom evaluation. Longitudinal follow-up at annual field office visits includes a detailed questionnaire, classification of asthma severity, and pre- and post-bronchodilator spirometry. Data from the panel studies provide estimates of short-term responsiveness to ambient pollutants for each subject;the effect estimates for each panel are the principal "exposure" for the longitudinal analysis of asthma severity and lung function growth. The study has generated a unique body of detailed exposure and individual follow-up data that are otherwise not currently available. Strength is the use of statistical methods that address many limitations of previous studies. The results of the proposed study will contribute important information to the effort to control the burden of asthma through reductions in air pollution.